Chlorofluorocarbons (i.e., CFCs) are compounds containing only carbon, fluorine and chlorine. Various CFCs have been used for many years as refrigerants, heat transfer media, foam expansion agents, aerosol propellants, solvents and power cycle working fluids. However, there has been recent concern that CFCs may be detrimental to the Earth's ozone layer. Consequently, there is a worldwide effort to find alternative compounds which contain fewer or preferably no chlorine substituents. The hydrofluorocarbon difluoromethane has been proposed as a replacement for some CFCs, particularly, in refrigeration, air-conditioning and other applications (see e.g., European Patent Application Publication No. 508,660 A1). Accordingly, there is interest in developing efficient processes for the production of HFC-32.
Japanese Patent Publication 59-225131 discloses preparation of HFC-32 by reacting dichloromethane with HF in the vapor phase at 200 to 500.degree. C. in the presence of a catalyst which consists of chromium fluoride or which has been obtained by molding a mixture of chromium fluoride and a carrier or by supporting chromium fluoride on a carrier. Chromium fluoride may be obtained by fluorinating a chromium-containing compound. Immersion of activated carbon in a solution of chromium chloride, followed by treatment with HF is disclosed (see e.g., Example 2). It is well known that activated carbon typically has an ash content comprising metal-containing compounds (e.g., potassium and sodium oxides) and other impurities (see e.g., M. Smisek et al. "Active Carbon", pages 61-70 (1970) and J. W. Hassler "Activated Carbon", pages 344-345 (1963)).
1,1-Dichlorotetrafluoroethane (i.e., CCl.sub.2 FCF.sub.3 or CFC-114a) is of interest as an intermediate for producing 1,1,1,2-tetrafluoroethane (i.e., CF.sub.3 CH.sub.2 F or HFC-134a). CF.sub.3 CH.sub.2 F can be obtained by the catalytic hydrogenolysis of CCl.sub.2 FCF.sub.3 using a supported metal hydrogenation catalyst (see e.g., C. Gervasutti et al., J. Fluorine Chem., 1981/82, 19, pgs. 1-20). The HFC-134a is an environmentally acceptable potential replacement for CFC refrigerants, blowing agents, aerosol propellants and sterilants that are implicated in the destruction of stratospheric ozone.